Tony Lit donated £4,800 to Labour last month

David Cameron suffers a major setback today as an opinion poll gives Labour its biggest lead over the Conservatives since he became Leader of the Opposition.

The survey for The Sunday Telegraph puts Gordon Brown's party on 40 per cent, a significant seven points ahead of the Tories, who are on 33 per cent, with the Liberal Democrats trailing on 19 per cent.

The clear evidence of a stronger than expected "Brown bounce" following the new Prime Minister's arrival at No 10 comes amid further bad news for the Tories as it can be revealed that their candidate in Thursday's Ealing Southall by-election donated £4,800 to Labour only last month.

Tony Lit, a wealthy radio station boss parachuted in to fight the seat by Mr Cameron, paid for a table at a Labour fundraising dinner at which he was pictured next to a smiling Tony Blair days before his departure as prime minister.

The revelations are certain to embarrass Conservative high command before polling in Ealing Southall, where Labour's majority at the 2005 general election was 11,440 but where Mr Lit has hopes of snatching the seat.

The ICM survey gives some comfort to Mr Cameron as it shows a significant level of public backing for plans to give tax breaks to married couples, outlined in a policy document published last week by the party's former leader, Iain Duncan Smith.

Sunday Telegraph